Microcomputers which are typically used today integrate read only memory (ROM) and electronic erasable programmable read only memory (EEPROM) onto an integrated circuit or chip to provide both program space and user configurable non-volatile storage area. Current portable electronic devices such as cellular telephones or radios require permanent write once, read many storage areas for serial numbers and subscriber billing information. These numbers must remain secure to prevent persons from accidentally or maliciously making changes to defeat billing mechanisms.
A variety of systems have been used in the prior art to allow a memory cell to be written to only once while reading from the cell any number of times. One technique designated one-time programmable (OTP) ROM uses an ultra-violet EEPROM. This involves using ultraviolet light to program and/or erase data in a memory device. When an opaque molding is used with the die holding the memory device, ultraviolet light is prevented from contacting the memory cells effectively shielding the cells and preventing them from being programmed or erased. Although this technique offers advantages in providing a adequate level of security, it involves many extras processing steps when manufacturing the memory as well has a high part cost in view of the opaque molding which must be used.
Thus, the need exists to provide a memory device which provides a high level of security without the burden of extra processing steps to implement and/or utilize ultra-violet EEPROM.